Rotary Vane Compressor or Vane Blower
The rotary compressor is adaptable to direct drive by induction motors or multicylinder gasoline or diesel engines. The units are compact, relatively inexpensive, and require a minimum of operating attention and maintenance. They occupy a fraction of the space and weight of a reciprocating machine of equivalent capacity. Rotary compressor units are classified into three general groups, slide vane-type, lobe-type, and liquid seal ring-type.
Construction and Working of Vane Compressor :
- It consists of a rotor mounted eccentrically in a circular casing and is supported by ball and roller bearings in the end cover of the body as shown in Fig.
- A set of spring-loaded vanes made of non-metallic material (i.e fiber or carbon) are mounted in slots on the rotor.
- When the rotor rotates; the centrifugal force acts on the vanes which throw the vanes out to make contact with the casing for all angular positions of the rotor.
- The vanes divide the space between the rotor and casing into a number of compartments.
- Two consecutive vanes form one compartment and due to the eccentric motion of the rotor the volume of each compartment keeps on changing.
- The suction side opens to the large area of vanes; thus as the rotor rotates; the volume of air V1 at pressure P1 is trapped between the vanes of rotor and casing.
- The delivery side opens to a much smaller; thus the space between the rotor and casing reduces and air has reduced volume V2 and increased pressure P2.
- The half of the total pressure rise takes place by internal reversible compression before the entrapped air is open to the delivery port.
- The air is further compressed in an irreversible manner due to momentarily backflow of high-pressure air from the receiver.
- The P-V diagram for this compression process of a vane compressor is shown in Fig.
Work done by vane Compressor :
Work done equation
In the compression process, 1 – 2; the volume is reduced from V1 to V2, and pressure is increased from P1 to P2 and follow according to the law PV ^γ = C.
In the compression process 2 – 3, due to the backpressure from the already compressed air from the receiver is assumed to be at constant volume.
Total work done during process 1-2 and 2-3 for X number of vanes is given by,
Applications of Vane Compressor :
The applications of vane compressor or vane blower is as follows,
1) Use for capacity up to 150 m3/min.
2) Pressure ratio up to 9 bar.
Advantages of Vane Compressor :
The advantages of vane compressor or vane blower is as follows,
1) The rotor and the vanes are only moving parts in the compressor.
2) No valves are required.
3) Discharge is complete and there is no clearance volume.
4) The operation is positive displacement as the gas is drawn in, trapped, and positively displaced by the movement of the vanes.
Disadvantages of Vane Compressor :
The Disadvantages of vane compressor are as follows,
1) The pressure involved in forcing the vanes back into the rotor will cause some vibration.
2) The speed is limited to 3000 rpm.
3) Lubrication must require at the vane tip to reduce the friction between vanes and casing.
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